The present invention relates to pyroelectric detectors. In particular, the present invention relates to improved fabrication techniques for high performance infrared pyroelectric detectors.
Pyroelectric detectors are a class of thermal detectors which have been the object of considerable research and development effort in recent years. When a pyroelectric detector views an infrared source, the temperature of the pyroelectric detector is altered. This temperature change causes a change in spontaneous polarization of the detector material, which, in turn, causes a charge to flow.
Ideally, a pyroelectric detector would be "free hanging" so that thermal loss to the surroundings would be by radiative transfer only. The free hanging detector has maximum responsivity.
In actual use, the ideal free hanging structure is not practical. The pyroelectric detector must be mounted in some manner to a substrate. Heat diffusion into the substrate causes a degradation of the responsivity of the pyroelectric detector at low frequencies. The effects of mounting a pyroelectric detector on a substrate have been discussed by B. R. Holeman, Infrared Physics, 12, 125 (1972).
The achievement of high detectivity pyroelectric detectors depends strongly upon the ability to fabricate a pyroelectric detector having a thickness of less than about 10 microns and the development of a mounting scheme in which the detector approximates a free hanging device. The requirement of a very thin device complicates the mounting of the detectors.
One technique for reducing thermal losses to the substrate is to provide a substrate having an opening. The pyroelectric detector is mounted over the opening so that only the outer edge of the pyroelectric detector is actually bonded to the substrate. Examples of this approach are shown in U.S. Pat. No. 3,571,592 by A. M. Glass and in British Pat. No. 1,337,735 by Keve et al.
While the mounting of a pyroelectric detector over a hole or cavity in a substrate does reduce thermal loss effects, it also complicates fabrication of the detector. Detector fabrication becomes particularly difficult when very small and very thin pyroelectric detector elements are fabricated. Batch fabrication of pyroelectric detectors and detector array fabrication is particularly difficult.